There are statutory requirements for permissible pollutant emissions of vehicles (in particular CO2, CO, NOx and number of particles), e.g. Regulation (EC) No 715/2007 of the European Parliament and of the Council, in which the Euro 5 and Euro 6 Standards are defined. Hitherto, standardized test cycles (e.g. the New European Driving Cycle (NEDC)) on test benches have been used to check that vehicles satisfy these statutory requirements. For this purpose, the emissions generated during the test cycle are sampled at the test bench and examined. The problem in this case is that the conditions on the test bench, under the standardized test cycle, are not comparable with the actual conditions when the vehicle is moving on an actual road. Therefore, a vehicle may satisfy the statutory requirements on the test bench, but nonetheless overstep said requirements during actual operation.
In order to prevent this, legislators are attempting to move the process of checking the predetermined pollutant emissions threshold values from the test bench to the actual road. This requires the pollutant emissions to be measured and checked during an actual journey of the vehicle, on an actual road, using Portable Emissions Measurement Systems (PEMS). There is therefore no longer a standardized test cycle, because a journey on a public road in normal traffic is always subject to random influences. In this case the legislators' aim is that a vehicle should satisfy the pollutant emissions threshold values under normal operating conditions, and not only on the test bench. The legislators also specify requirements for assessing the pollutant emissions after the test drive, e.g. the use of specific data analysis tools.
For this purpose, the legislators have defined a Real Driving Emissions (RDE) test procedure. Therein specific requirements for the vehicle weight, the ambient temperature and the geographical altitude at which the test drive should take place are specified only. In addition, the proportions of the test procedure that should be made up by different driving situations is also defined, for example 33%±10% division among town, country and motorway, but at least 16 km each, vehicle speed in the country in the range of 60-90 km/h, test drive length 90-120 min, etc. Since this check is to be carried out on a public road, each test drive is also subject to random influences, such as other traffic, traffic lights, etc. It is immediately clear therefrom that an actual test drive is not reproducible, but instead in each case constitutes a more or less random chain of events.
This paradigm change also has a direct influence on vehicle manufacturers when developing new vehicles.
Hitherto, each development step could be checked on the test bench, using the standardized test cycles. For this purpose, it was merely necessary for the relevant test specimen to undergo the test cycle and the pollutant emissions to be examined after each development step. This is no longer possible with the new RDE test procedure, since it is in principle not possible to predict whether a newly developed vehicle will pass the RDE test procedure, once the development has been completed, by satisfying the pollutant emissions threshold values. Only the finished vehicle can be driven on the actual road, i.e. the RDE test procedure can be carried out only at the very end of the development. If the vehicle does not pass this check, this would obviously have a huge impact on the vehicle manufacturer which, in an extreme case, would have to repeat a year-long development at least in part, at huge cost and outlay.
It is also of no help to use the previous standardized test cycles during the vehicle development, since the pollutant emissions threshold values being satisfied when standardized test cycles of this kind are applied does not automatically guarantee that these threshold values will be satisfied under the RDE test procedure.
Of course, it would be possible to combine all the possible operating states of a vehicle in one test scenario and use this test scenario to check each development step. However, this is hardly expedient, since implementing a test scenario of this kind on a test bench would take a very long time, and this would slow the development, increase the test bench times, and would be very complex overall. Constructing a test scenario arbitrarily is likewise not expedient, since it would not be possible to guarantee thereby that the statutory requirements would be satisfied under the RDE test procedure.
Furthermore, not every driving maneuver, e.g. accelerating from a low engine speed, overtaking on a country road, turning in urban traffic, etc. will necessarily have the same impact on the pollutant emissions in every vehicle. This means that a test scenario may be suitable for one specific vehicle, but not for a different vehicle.
The above in principle also applies in the same way for other target variables of the development of a vehicle, for example the consumption of a vehicle, although there are no statutory requirements in this regard (or at least not yet). However, the consumption is generally also a development aim when developing a vehicle, and therefore here, too, the aim is to achieve the desired consumption, for example in the RDE test procedure.
In the same way, there may also be further target variables of development, in addition to the pollutant emissions or the consumption, such as the acoustics of the vehicle, the drivability of the vehicle or the durability of the vehicle. Here, too, there is a need to construct suitable tests which make it possible to carry out tests on a test bench even in early development steps in order to guarantee, as far as possible, a later passing of a predetermined test procedure or the satisfying of a specified value for a target variable.